1. Field of the Invention
The present invention relates to a loop-shaped antenna and a surface-mounted antenna to be mounted on a circuit board of communication equipment, for example, and the communication equipment having such an antenna.
2. Description of the Related Art
A conventional antenna of this type includes a plurality of radiant electrodes. Each of the radiant electrodes has a resonance frequency band that is different from each other so as to transmit or receive each of a plurality of signals having different resonance frequency bands. As a result, one antenna having a plurality of radiant electrodes can transmit or receive signals with a plurality of frequency bands.
However, in such an antenna, miniaturizing of the antenna is difficult because of the need to have a plurality of radiant electrodes.
FIG. 6 is a schematic perspective view of an example of a surface-mounted antenna. In a surface-mounted antenna 20, a base member 21 made of a dielectric substance is provided with a feeding radiant electrode 22 arranged to extend from a bottom surface 21a toward a side surface 21d via a side surface 21b and a top surface 21c. A metallic plate 24 is attached to the base member 21 with one end connected to the feeding radiant electrode 22. The other end of the metallic plate 24 is an open end. In the surface-mounted antenna 20, one radiant electrode is defined by the feeding radiant electrode 22 and the metallic plate 24.
Such a surface-mounted antenna 20 is connected on a substrate 25 of an object to be mounted (a circuit board of communication equipment, for example) by soldering using the bottom surface 21a of the base member 21 as a mounting surface. The base member 21 is provided with a fixing electrode 23, which is to be a base electrode for soldering. The fixing electrode 26 may be grounded or may not be grounded on the substrate 25 of the object to be mounted (mounting substrate) depending on a circuit of the mounting substrate 25.
The feeding radiant electrode 22 is connected to a signal supply source 27 via a matching circuit 26 by mounting the surface-mounted antenna 20 on the mounting substrate 25 exactly as designed. Supplying a signal from the signal supply source 27 to the feeding radiant electrode 22 via the matching circuit 26 transmits the signal to the metallic plate 24 via the feeding radiant electrode 22. By the signal supply, the feeding radiant electrode 22 and the metallic plate 24 produce resonance so as to perform an antenna operation (that is, transmitting or receiving of a signal).
As noted above, the radiant electrode has a plurality of resonant frequencies that are different from each other so as to be able to produce resonance at each of the frequencies. Accordingly, in order to make an antenna applicable to a plurality of communication systems, it is under consideration that one radiant electrode is made to perform a higher-order-mode antenna operation with a frequency higher than that of a basic-mode as well as perform the basic-mode antenna operation (that is, operation of transmitting or receiving of a signal), by utilizing not only the resonance with the basic lowest resonance frequency of the radiant electrode but also the resonance with a higher-order-mode resonance frequency higher than that.
However, in the structure of the surface-mounted antenna 20, it has been difficult to satisfactorily perform the higher-order mode antenna operation because of insufficiency in a gain.
Since the mounting substrate is assumed to be a grounded plane, in the structure of the surface-mounted antenna 20, an unnecessary capacitance is produced between the metallic plate 24 and the mounting substrate 25. There is a problem that the antenna gain is liable to deteriorate because of the unnecessary capacitance between the metallic plate 24 and the mounting substrate 25.
In order to solve the above-described problems, preferred embodiments of the present invention provide a miniaturized loop antenna having only one radiant electrode that is capable of transmitting or receiving signals with a plurality of frequency bands that are different from each other so as to perform a basic-order-mode antenna operation and a higher-order-mode antenna operation and a communication apparatus including such a novel antenna.
According to one preferred embodiment of the present invention, a loop antenna includes a linear radiant electrode for performing an antenna operation, one end of the radiant electrode being a feeding end for receiving a signal from a signal supply source and the other end being an open end, wherein the radiant electrode has a substantially loop shape, in which a feeding-end portion and an open-end portion are arranged adjacent to each other with a spaced defined therebetween, and wherein the radiant electrode is provided with a short-cut electrode short-cutting a loop of the radiant electrode.
Preferably, the loop of the radiant electrode extending from the feeding end toward the open end has an electrical length corresponding to a predetermined basic-mode resonance frequency while a short loop extending from the feeding end of the radiant electrode toward the open end via the short-cut electrode has an electrical length corresponding to a higher-order-mode resonance frequency higher than the basic-mode resonance frequency, such that the radiant electrode performs a basic-mode antenna operation and a higher-order-mode antenna operation.
Preferably, the radiant electrode is narrow plate-shaped instead of being linear shaped.
According to this preferred embodiment of the present invention, the wire or narrow plate-shaped radiant electrode is formed to have a substantially loop shape by arranging a feeding-end portion and an open-end portion adjacent to each other with a space provided therebetween. The radiant electrode is provided with the short-cut electrode short-cutting the loop of the radiant electrode. The loop extending from the feeding end of the radiant electrode toward the open end has an electrical length corresponding to the established basic-mode resonance frequency while the short loop extending from the feeding end of the radiant electrode toward the open end via the short-cut electrode has an electrical length corresponding to the established higher-order-mode resonance frequency, so that the radiant electrode can perform predetermined basic-mode and higher-order-mode antenna operations.
That is, signals with predetermined plural frequency bands can be transmitted or received by providing only one radiant electrode, so that the miniaturizing of the antennal can be facilitated in comparison with an antenna having plural radiant electrodes.
In the loop antenna according to this preferred embodiment of the present invention, an electrical length of the loop (basic loop) extending from the feeding end of the radiant electrode toward the open end determines the basic-mode resonance frequency of the radiant electrode while the short loop extending from the feeding end of the radiant electrode toward the open end via the short-cut electrode determines the higher-order-mode resonance frequency of the radiant electrode. The electrical length of the short loop can be changed and set by adjusting the arrangement and length of the short-cut electrode independently of the electrical length of the basic loop. That is, the electrical length of the basic loop and the electrical length of the short loop can be changed and set separately from each other. Therefore, the basic-mode resonance frequency of the radiant electrode and the higher-order-mode resonance frequency can be adjusted and set to independently have the respective established frequencies. Thereby, the design of the radiant electrode is extremely flexible and easy so as to easily allow for and accommodate many design changes.
In contrast, in a conventional antenna, when the radiant electrode is to perform an antenna operation by using higher-order-mode resonance frequencies other than the lowest resonance frequency among the plural resonance frequencies of the radiant electrode, it is very difficult to use the higher-order-mode antenna operation because the gain in the higher-order-mode antenna operation is extremely small.
Whereas, according to the present preferred embodiment of the present invention, the feeding-end portion and the open-end portion of the radiant electrode are arranged adjacent to each other with a space defined therebetween, so that the feeding-end portion and the open-end portion are combined with a capacitance therebetween. By the capacitance combination, the gain in the higher-order mode is greatly improved so as to achieve the using the higher-order-mode resonance frequency of the radiant electrode to the signal transmission or receiving.
Furthermore, according to the present preferred embodiment of the present invention, the feeding-end portion and the open-end portion of the radiant electrode are combined with a capacitance therebetween, so that an electric field can be confined within the loop of the radiant electrode. As a result, reduction in the frequency bandwidth and the deterioration in the gain due to the electric field captured to the ground is reliably prevented. In particular, such reduction in the frequency bandwidth and deterioration in the gain are liable to occur in the higher-order-mode side. However, by the electric field confining effect due to the loop shape of the radiant electrode, these problems are prevented from occurring.
According to another preferred embodiment of the present invention, a surface-mounted antenna includes a base member having a feeding electrode to be connected to a signal supply source, an open electrode arranged substantially parallel to the feeding electrode leaving a space in a floated state from the ground, and a linear electrode attached to the base member with one end connected to the feeding electrode and with the other end connected to the open electrode, wherein a loop-shaped radiant electrode extending from the feeding electrode toward the open electrode via the linear electrode is defined by the feeding electrode, the linear electrode, and the open electrode, and wherein the linear electrode is provided with a short-cut electrode for short-cutting a loop of the radiant electrode.
Preferably, the loop of the radiant electrode extending from the feeding electrode toward the open electrode via the linear electrode has an electrical length corresponding to a predetermined basic-mode resonance frequency and a short loop extending from the feeding electrode of the radiant electrode toward the open electrode via the linear electrode and the short-cut electrode has an electrical length corresponding to a predetermined high-order-mode resonance frequency higher than the basic-mode resonance frequency so that the radiant electrode performs a basic-mode antenna operation and a higher-order-mode antenna operation.
Preferably, the base member is provided with a frequency-adjusting electrode arranged adjacent to one of the feeding electrode and the open electrode leaving a space for adjusting the resonance frequency of the radiant electrode by being combined with the adjacent electrode with a capacitance therebetween.
Preferably, the base member is provided with a narrow plate-like electrode instead of the linear electrode.
According to the present preferred embodiment of the present invention, the substantially loop-shaped radiant electrode extending from the feeding electrode toward the open electrode via the linear electrode is configured by the feeding electrode and the open electrode, which are disposed in the base member, and the linear electrode attached to the base member. The feeding electrode and the open electrode are arranged adjacent to each other leaving a space, so that the feeding electrode and the open electrode are combined with a capacitance therebetween. In other words, the substantially loop-shaped radiant electrode is arranged such so that a feeding-end portion (feeding electrode) and an open-end portion (open electrode) are combined with a capacitance therebetween.
By this configuration, the gain in the higher-order-mode antenna operation of the radiant electrode is greatly improved. That is, not only the resonance at the basic-mode resonance frequency of the radiant electrode but also the resonance at the higher-order-mode resonance frequency can be sufficiently utilized as antenna operations. Thereby, signals with a plurality of different frequency bands can be transmitted or received by only one radiant electrode.
Also, according to the present preferred embodiment of the present invention, the linear electrode is provided with the short-cut electrode short-cutting the loop of the radiant electrode. By providing the short-cut electrode, the radiant electrode has the short loop extending from the feeding electrode toward the open electrode via the linear electrode and the short-cut electrode. By configuring the short loop of the radiant electrode to have an electrical length corresponding to the established higher-order-mode resonance frequency and by configuring the basic loop of the radiant electrode extending from the feeding electrode toward the open electrode via the linear electrode to have an electrical length corresponding to the established basic-mode resonance frequency, the radiant electrode can perform predetermined basic-mode and higher-order-mode antenna operations.
The basic-mode resonance frequency of the radiant electrode is determined by the electrical length of the basic loop while the higher-order-mode resonance frequency is determined by the electrical length of the short loop. By changing the arrangement and length of the short-cut electrode, the electrical length of the short loop can be changed, whereas the electrical length of the basic loop is not changed. Therefore, by changing the arrangement and length of the short-cut electrode, the higher-order-mode resonance frequency of the radiant electrode can be changed independently of the basic-mode resonance frequency. Thereby, the resonance frequencies of the basic mode and higher-order-mode of the radiant electrode can be easily changed and adjusted so as to promptly correspond to the design change, for example. Also, by providing the frequency-adjusting electrode in the base member, the adjustable range of the resonance frequency of the radiant electrode can be expanded.
Furthermore, according to the present preferred embodiment of the present invention, the feeding electrode (feeding-end portion) and the open electrode (open-end portion) of the radiant electrode are combined with a capacitance therebetween, so that an electric field can be confined within the loop of the radiant electrode. Thereby, reduction in the frequency bandwidth and the deterioration in the gain due to the electric field captured to the ground are reliably prevented. In particular, such reduction in the frequency bandwidth and deterioration in the gain are liable to occur in the higher-order-mode side. However, by the confining effect of the electric field due to the loop shape of the radiant electrode, these problems are reliably prevented from occurring.
Furthermore, in the narrow plate-shaped electrode changed from the wire electrode, the narrow plate-shaped electrode is manufactured preferably by punching a metallic plate using a die. In this case, the narrow plate-shaped electrode can be easily manufactured, thereby improving the productivity of the electrode.
Moreover, the electrodes attached to the base member have unnecessary capacitances to a substrate to be mounted, which is assumed as the ground. However, according to a preferred embodiment of the present invention, the electrodes attached to the base member have wire or narrow plate shapes, and thus the unnecessary capacitances to the ground are minimized. Thereby, the deterioration in the antenna gain due to the unnecessary capacitances between the electrode and the ground are prevented.
In another preferred embodiment, a communication apparatus includes one of the antennae according to the preferred embodiments described above.
In a communication apparatus having an antenna according to preferred embodiments of the present invention, by the miniaturized antenna, the communication apparatus can be easily miniaturized. The reliability of the communication apparatus is also greatly improved.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.